Clean name for new output directory
Clean name for new output directory

The font may be saved below in the file tree and therefore the new direcotry will start with `../` which is by default a invisible file. E.g.
```
ocropus-linegen -t ../text-generation/text.txt -f ../text-generation/font.ttf -m 5 -o ../text-generation/linegen
```
will create a directory `/text-generation/linegen/.._font/`.

This should be an easy and safe fix.
kba/ocropy,amitdo/ocropy,tmbdev/ocropy,amitdo/ocropy,loveheaven/ocropy,zuphilip/ocropy,olivernina/ocropy,stweil/ocropy,olivernina/ocropy,tmbdev/ocropy,stweil/ocropy,stweil/ocropy,tmbdev/ocropy,olivernina/ocropy,kba/ocropy,zuphilip/ocropy,loveheaven/ocropy,amitdo/ocropy,zuphilip/ocropy,kba/ocropy,loveheaven/ocropy